Hmmm, a 12' radius 2v dome implies strut lengths of 88.99 (x35) and 78.70 (x30) inches (thanks Tara!).
I haven't actually built a 2v dome so can't comment on the structural strength of struts this long in various diameters, but my intuitiion says that 3/4 inch conduit might be a bit thin for those lengths, but 1 inch should be OK (your actual mileage may vary). Certainly, using 3/4 inch conduit would mean not hanging anything of much weight from either the vertices or (goodness, no!) the middle of the struts.
3/4 inch conduit is around $2.25 from Home Depot. 1 inch conduit is $3.75 the last time I checked (couple of weeks back).
Choosing strut lengths that don't in some way add up to around 120 inches (the length of conduit from places like HD) means you will need 65 pieces, plus a few spares; 70 is a good number. So, approximately $157.50 plus tax for 3/4 inch struts, or $262.50 for 1 inch. Just remember, with this approach you are going to have 70 shorter pieces of conduit left over.
In all honesty, for the size dome you want I recommend a 5/8 3v dome built with a 142 inch radius, which means the struts work out really well, so you only end up needing about 85-90 pieces of conduit, and they can all be 3/4 inch with fewer structural worries (you still won't be able to climb on it if you weigh anywhere near what I do, but you will be able to hang hammocks & such from the vertices). Plus, the walls will be much straighter for the first few feet meaning all the space is useable, and the ceiling is higher giving more room for hot air to rise. So, for basically less than you would pay for 1 inch conduit in a 2v dome (but a bit more in other materials and labor, see below) you can have a dome that is "much better" (IMHO <g>).
Then there are bolts; for a 2v it looks like you will need 26 - 3/8 x 2.5 inch bolts, 52 washers, and 26 nuts. At that number they are probably almost cheaper in boxes of 50 than buying them individually. I use Grade 8, which is structurally overkill, but the threads don't get dinged as easily. Can't remember off the top of my head what a box of 50 grade 8 2.5x3/8 goes for, but figure on $0.20 apiece in bulk or $0.30 apiece separately, or about $10 for the bolts, and I am guessing $0.05 per washer, or $5.00 for 100, and $0.10 per nut, or $5 for 50. So, about $20-$25 in nuts & bolts. Using Grade 5 will lower that substantially, to maybe $15 or less.
For a 3v 5/8 you will need 61 bolt assemblies.
Next is rebar. I use 2 foot sections from Orchard Supply, or you can buy longer pieces and cut them (especially if you use a cutoff wheel, see below). Can't remember how much rebar is these days, but figure on $1 a foot for 1/2 inch, and you will need 10 pieces for a 2v dome, or 15 for a 3v, or $20 to $30.
Then there is paint to keep the ends from rusting once you cut & drill them. Using different colors for the different length struts really helps. I use iindustrial Rustoleum in flat colors, about $5 per can from HD, and one can will be plenty for several builds of your dome (you will want to respray the ends upon dissassembly each time because they get all scratched up no matter how careful you are). So, $10 in paint for a 2v dome or $15 for a 3v.
Then there are construction tools that you might not already have, like:
Pipe cutter, anywhere from $7 for a cheap one you probably won't like to $35 for a Rigid that you will like, but probably can't really justify for this many cuts. Plus, using a pipe cutter is a pain in the shoulder after awhile. I personally gave up on using a pipe cutter and now solely use a cutoff wheel on my 7 1/2 inch circular saw. Lots of sparks, but one $3 wheel will cut hundreds of pipes & rebar if you are careful and don't wreck the blade.
Next is something to flatten the ends. I use this on my workbench:
http://www.harborfreight.com/cpi/ctaf/D ... umber=4711
It works great and the press plates last for a few hundred presses. Cost is $70 plus tax & handling.
Then you will need to drill those holes. I think a drill press is well justified for this task, even if you go cheaper on the other tools, because getting the strut lengths just right really helps make the assembly go smoother. A decent drill press can be had for under $100. Here is one that should do the trick:
http://www.harborfreight.com/cpi/ctaf/D ... mber=44836
You will need a couple of C-clamps or a vise or two to make a jig and secure the poles during drilling. You probably have those laying around.
For drill bits I swear by 7/16 inch 135 degree cobalt and lots of cutting oil (after screwing up a titanium nitride bit and the first cobalt bit learning how to work a drill press properly). Harbor sells sets of cobalt bits, but I do not know of their quality. I buy mine from a local specialty outlet for $15 apiece and one bit is good for several hundred holes as long as you drill slowly, use lots of cutting oil and let the drill bit cut the conduit rather than just heating it up and boring through (this latter will wreck the bit after a hundred holes or so; you can still drill, but you are basically heating and punching rather than drilling at that point, and it takes longer; I am one of those obsessive types who counts time while waiting for completion; any shorter than 50 seconds per hole and I am drilling too fast; any longer than 60 seconds and the bit has gone dull). One of the items on my list is a bit sharpener, but the good ones are pricey.
Next, I use a benchtop grinder with a medium grain wheel and a wire buffer wheel to grind off any drill flash and smooth/round the ends a bit. Here's one that should do the trick:
http://www.harborfreight.com/cpi/ctaf/D ... mber=37822
And 6 inch buffer wheels are about $7 at Home Despot.
Oh, and you'll need some 9/16 inch sockets & wrenches to do the assembly. You probably have those. And a 10 inch Vise Grip (about $10) or two will come in handy. And maybe a sledge (4 lb is good, $9) to pound the rebar. And some rope to bundle up the struts and lash the rebar and what not; maybe $10 worth of 1/4 inch nylon.
So, there are some base numbers based on current prices (as of January, 2004). You can probably take it from there. And there are lots of sites that discuss dome design and fabrication. The best, IMHO, is Tara's site, at:
Oh, fab time. It takes me approximately 10 minutes per pole to do the cutting, flattening, drilling, grinding, bending and painting, on average. So figure on around 12 hours for a 2v dome and 25-30 hours for a 3v dome, assuming you excel at switching between thinking tasks and drone type tasks easily.
All the Best,
D (aka Usually Harmless)